1. Field of the Invention
The present invention relates to a multiple bag (or container) comprising a plurality of bags which are linked with each other. The multiple bag is used, for example, as a blood bag for separating whole blood into blood constituents.
2. Description of the Related Art
For the reason of an effective utilization of blood and reduction of physical load with which a patient to be transfused may be burdened, the blood transfusion system now in use comprises steps of centrifugally separating whole blood obtained from a donor into different constituents and transfusing only necessary constituents to the patient. The introduction of such a constituent transfusion system permits more effective use of blood than in the conventional system utilizing unseparated whole blood.
A multiple bag comprising a donor bag (a blood collection bag) and one or more different bags is used in the constituent transfusion.
For example, a triple bag comprised of a blood collecting bag, a platelet concentrate bag (hereinafter referred to as PC bag) for preserving platelet and a plasma preserving bag (hereinafter referred to as plasma bag), these bags being connected with each other by tubes. A blood collected in the blood collection bag is subjected twice to centrifugal separation to be separated into three different constituents such as erythrocyte component, thick platelets component, and thin platelets component, and these constituents are contained for preservation in the donor bag, PC bag, and plasma bag respectively.
The respective bags constituting such a multiple bag are produced by overlaying sheet materials of soft polyvinyl chloride, and fusion bonding them together at the peripheral edges, and these bags are generally subject to high-temperature and high-pressure steam sterilization (autoclave sterilization). In order to avoid any blocking which may occur between the inner surfaces of the opposite sheets of the bags during the autoclave sterilization, the sheets are treated for embossing so that they may have a surface roughness (Rz) ranging around from 15 .mu.m to 50 .mu.m.
In view of the production control and cost as well, these bags are produced from the same sheet materials.
with such a multiple bag, there lies problems that it gives rise to adhesion of the blood constituents (erythracyte, leukacyte, platelet) to the inner surface of the bag sheet, and to excessive remaining of blood within the bag when the blood is removed.
An earnest and deep study by the present inventor of these phenomena revealed that such phenomena are considerably observed if the inner surface of the bag sheet is subjected to deeper embossment, or fine projections are formed more greatly in height on the inner surface of the sheet.
In this connection, it seems effective to use a sheet with the inner face having fine projections of less height or being less rough. In the case, however, it causes insufficient preventive effect of blocking between the sheets on the contrary.